The present invention relates to the field of hydrocarbon production, and more particularly to the triggering of explosive devices in well bores to perforate well casings, set packers, and accomplish other work. Most particularly, the invention relates to a method and apparatus for the control of downhole explosive devices utilizing a physical structure such as a slickline, wireline, tool string, or conduit to transmit non-electrical control signals to a explosive device positioned in the wellbore.
In oil and gas exploration and production operations, well bores are drilled into the ground to gain access to subsurface hydrocarbon-bearing formations or reservoirs. The well bores are typically lined with steel tubing, known as casing or liner, to provide the wellbore with a stable, permanent barrier. This casing is often secured by cement that is pumped into the annulus between the outside diameter of the casing and the inside diameter of the wellbore wall.
While the casing stabilizes the wellbore wall, it also seals the fluids within the earth strata. Thus, the casing must be opened in order to allow inflow of hydrocarbons into the casing for extraction. To selectively open the casing to such fluid flow, the casing wall is often penetrated in the region of a fluid production zone by shaped or oriented charge explosives, which when detonated, penetrate the casing creating perforations through which fluid in the formation may flow. The tubular tool section that carries these explosives is often referred to as a “perforation gun” or more simply as a “gun.”
By traditional prior art procedure, the tubular gun may be releasably attached to the end of a wireline or coiled tube for running into the well. When the gun has been positioned at the desired depth, the gun may be secured in place and “armed” for firing.
The use of explosives for these various downhole purposes has certain drawbacks. Explosive devices positioned within a wellbore which fail to fire or for some reason are not fired must be retrieved from the wellbore in its unfired condition, creating a potential hazard to both personnel and the wellbore. Likewise, inadvertent firing of an explosive device or self-detonation of an explosive device downhole while the gun is being positioned or retrieved can damage the wellbore, such as perforating the casing at an undesired depth.
Thus, it is common to utilize some type of mechanism to arm and/or fire the gun. For example, hydraulic manipulation of mechanical components of the tubular string is often used to trigger or fire such guns. The prior art further includes downhole triggering/firing control devices that are operable by pressure, time or motion, e.g., a line jerk, referring to a sharp jolt or jerk of the downhole device. Frequently, to ensure that a gun is not triggered at the wrong depth (such as during deployment), information is programmed into the triggering device based on the expected firing parameters at a desired position so that the triggering device becomes operable only when the expected parameter, such as depth, pressure, or temperature at the device, is satisfied.
There is a need for a downhole triggering system that can reliably prevent accidental or unintended detonation of a perforating gun and at the same time operate reliably when intended to operate.
It is desirable to provide a triggering system that allows complete depth control and triggering in an integrated system and avoids the likelihood of a triggering device programmed with incorrect triggering parameters. Such a device should permit the gun to be fired only under predictable circumstances.
It is further desirable to provide a system that operates in real time. By utilizing a real time clock onboard the trigger mechanism, the operator can more easily synchronize the operations of the downhole trigger with the operations on the surface. Heretofore, no such trigger mechanism includes a real time clock for operation.
Finally, it also desirable to provide a system that permits surface communication with the downhole trigger device without reliance on electrical communications or a “line jerk.”